Knock detector

Abstract

A comparator compares, either before or after being rectified, a signal obtained from the vibration signal representing the vibrations of a spark ignition internal combustion engine and which has passed through a signal transmitting circuit, with a reference level signal from a reference level signal forming circuit to produce a knock signal representing the occurrence of knocking when the former signal is greater in magnitude than the latter. The reference level signal forming circuit rectifies and smooths the vibration signal to produce a rectified smoothed signal, and includes a first amplifying circuit which amplifies the rectified smoothed signal to produce the reference level signal, mentioned above. When the engine speed is above a predetermined value, an engine speed determining circuit produces a drive signal to which a changeover circuit responds by changing the magnitude of at least one of the signal transmitting circuit and the reference level signal forming circuit from one value to another whereby possible knocking occurring in the overall range of higher and lower engine speeds is reliably detected for use in spark timing control in the spark ignition internal combustion engine.

What is claimed is: 
     
       1. A knock detector for a spark ignition internal combustion engine, comprising: a. a vibration sensor for sensing engine vibrations to produce a vibration signal corresponding to the vibrations;   b. means for transmitting therethrough a signal obtained from the vibration signal;   c. a reference level signal forming means including: 1. a rectifier for rectifying the vibration signal to produce a rectified signal;   2. an averaging means for smoothing the rectified signal to produce a smoothed signal; and   3. a first amplifying means for amplifying the smoothed signal to produce a reference level signal;     d. a comparator for comparing the signal from said transmitting means with the reference level signal to produce a knock signal representing the occurrence of knock when the former signal is greater in magnitude than the latter;   e. an engine speed determining means for sensing the engine speed to produce a drive signal when the engine speed exceeds a predetermined value; and   f. a changeover means responsive to the drive signal for changing the magnitude of the output of at least one of said transmitting means and the reference signal forming means such that the relationship in magnitude between the reference signal and the signal from the transmitting means before the drive signal is produced is maintained.   
     
     
       2. The knock detector as claimed in claim 1, wherein said first amplifying means includes an operational amplifier, an input resistor connecting the output of said averaging means to the inverting input of said operational amplifier, a first feedback resistor connecting the inverting input and output of said operational amplifier, and said changeover means includes a first change means responsive to the drive signal for reducing the resistance of said first feedback resistor. 
     
     
       3. The knock detector as claimed in claim 2, wherein said first change means includes a second feedback resistor and a first switching means responsive to the drive signal for connecting said second feedback resistor in parallel with said first feedback resistor. 
     
     
       4. The knock detector as claimed in claim 1, 2 or 3, wherein said transmitting means includes a second amplifying means for amplifying the signal obtained from the vibration signal, said second amplifying means having a first output resistor connecting the output of said second amplifying means to ground, and said changeover means includes a second change means responsive to the drive signal for reducing the resistance of said first output resistor. 
     
     
       5. The knock detector as claimed in claim 4, wherein the signal obtained from the vibration signal is a substantially unaltered signal. 
     
     
       6. The knock detector as claimed in claim 4, wherein the signal obtained from the vibration signal is a rectified signal. 
     
     
       7. The knock detector as claimed in claim 4, wherein said second change means includes a second output resistor and a second switching means responsive to the drive signal for connecting said second output resistor in parallel with said first output resistor. 
     
     
       8. The knock detector as claimed in claim 7, wherein the signal obtained from the vibration signal is a substantially unaltered signal. 
     
     
       9. The knock detector as claimed in claim 7, wherein the signal obtained from the vibration signal is a rectified signal. 
     
     
       10. The knock detector as claimed in claim 1, wherein said changeover means includes a first output resistor connecting the output of said first amplifying means to ground and a third change means means responsive to the drive signal for reducing the resistance of said first output resistor. 
     
     
       11. The knock detector as claimed in claim 2 or 3 wherein said changeover means includes an offset change means responsive to the drive signal for reducing an offset output of said first amplifying means. 
     
     
       12. The knock detector as claimed in claim 11, wherein the signal obtained from the vibration signal is a substantially unaltered signal. 
     
     
       13. The knock detector as claimed in claim 11, wherein the signal obtained from the vibration signal is a rectified signal. 
     
     
       14. The knock detector as claimed in claim 11, wherein said offset change means includes an offset voltage applied to the inverting input of said operational amplifier and a means responsive to the drive signal for reducing the magnitude of the offset voltage. 
     
     
       15. The knock detector as claimed in claim 14, wherein the signal obtained from the vibration signal is a substantially unaltered signal. 
     
     
       16. The knock detector as claimed in claim 14, wherein the signal obtained from the vibration signal is a rectified signal. 
     
     
       17. The knock detector as claimed in claim 14, wherein said offset change means includes series connected first and second offset resistors connecting the offset voltage to ground, a third offset resistor connecting the common junction between said first and second offset resistors to the inverting input of said operational amplifier, a fourth offset resistor, and a third switching means responsive to the drive signal for connecting said fourth resistor in parallel with said second offset resistor. 
     
     
       18. The knock detector as claimed in claim 17, wherein the signal obtained from the vibration signal is a substantially unaltered signal. 
     
     
       19. The knock detector as claimed in claim 17, wherein the signal obtained from the vibration signal is a rectified signal. 
     
     
       20. The knock detector as claimed in claim 10, wherein said third change means includes a second output resistor and a third switching means responsive to the drive signal for connecting said second output resistor in parallel with said first output resistor. 
     
     
       21. The knock detector as claimed in any one of claims 1, 2, 3, 10 and 20, wherein the signal obtained from the vibration signal is a substantially unaltered signal. 
     
     
       22. The knock detector as claimed in any one of claims 1, 2, 3, 10 and 20, wherein the signal obtained from the vibration signal is a rectified signal.